As a configuration for switching transmission of driving force in an image forming apparatus and the like, there are known configurations employing a one-way clutch, a torque limiter, an electromagnetic clutch, and the like.
However, when the one-way clutch is used, normal rotation and reverse rotation of a driving source need to be switched in order to control presence or absence of transmission of the driving force to the one-way clutch.
When the torque limiter is used, since presence or absence of transmission of rotational driving force thereof is switched on the basis of torque, the torque limiter cannot be applied when it is desired to change a driving force transmission path according to the number of revolutions.
When the electromagnetic clutch is used, a large arrangement space is required and, moreover, cost for adopting the electromagnetic clutch is relatively high.
Therefore, driving force transmitting mechanisms that switch power transmission using centrifugal force are disclosed in, for example, JP-A-10-318292 and JP-A-10-281188.
However, in the technique disclosed in JP-A-10-318292, power transmission is performed by frictional force when the number of revolutions exceeds a predetermined number of revolutions. The technique is not suitable for high-torque driving force transmission. Besides, heat is generated during the power transmission.
In the technique disclosed in JP-A-10-281188, switching of transmission of driving force from a driving shaft to a driven shaft is realized by a steel ball, movement of which in a rotation radius direction is controlled by magnetic force. However, noise is likely to occur when the steel ball comes into contact with a recess. Further, when it is attempted to realize high-torque driving force transmission, it is necessary to increase diameters of the steel ball and a guide hole and deepen the recess. However, such a configuration is likely to prevent a reduction in size of an entire apparatus.